Power systems, particularly internal combustion engines like diesel engines, gasoline engines and natural gas burning turbines, create byproducts and emissions during operation including nitrogen oxide emissions such as NO and NO2, sometimes represented as NOx. To reduce the amount or effect of the nitrogen oxides produced by the internal combustion engines, a process called selective catalytic reduction is employed in which exhaust gases, usually intermixed with a reductant agent, are adsorbed onto a catalyst substrate located downstream in the internal combustion engine. Although, catalyst substrates for locomotive engine applications are known, current emission regulations require stringent reduction of harmful emissions from large internal combustion engines. Examples of such large engines include generator sets and marine engines.
Because of the large amount of emissions produced by such engines, a catalyst substrate can have a cross-section area to adequately treat exhaust gases without producing undesirable back pressure on the engine. The current processes for manufacturing of catalyst substrates limit their cross section. Consequently, catalyst substrates for large engine applications are provided with a plurality of available catalyst substrates packed together to adequately treat exhaust flow without creating detrimental back pressure on the engine. However, these catalyst substrates, generally formed by extrusion process, have a large tolerance variation that requires complicated sorting to match parts for packaging in a specific size. This result in a wide variation in installation pressures that may damage catalyst substrate or bulge an outer canister which is generally adapted to group catalyst substrates with uniform sizes and shapes. Further, when such catalyst substrates are packed together to form a larger unit, there may be gaps between them because of variations in their dimensions. These gaps may provide passages through which the exhaust gases may leak untreated, which result in lower NOx conversion and the engine not meeting the required regulations.
US Patent Application Number 20110030355 A1, hereinafter referred to as the '355 application, relates to a catalytic converter cartridge comprising multiple square, rectangular or other flat sided catalyst coated substrates, each substrate of which has each of its flat sides covered by a compressible mat material. These mat-covered substrates or modules are arranged into a multiple module array enclosed within a metal shell with each module preferably separated from adjacent modules by sheet metal spacers.